The present invention relates to a transmission and, more particularly, to a multi-gear, multi-range transmission with an arrangement for preventing a range shift when the transmission is in reverse gear.
In certain vehicle transmissions, particularly manual vehicle transmissions for heavy vehicles, a first main section is provided and includes a plurality of gears to provide a plurality of different speed ratios. A second, auxiliary section is often provided that permits input torque from the first section to be modified from, for example, a first range to a second range to provide an additional set of speed ratios. Thus, a transmission having a main transmission section adapted to be shifted from neutral into, for example, one of five forward gear positions and one reverse gear position can have ten forward speed ratios and two reverse speed ratios by shifting from a low range to a high range.
The auxiliary or range section of the transmission typically has a shift collar functioning together with a synchronizer arrangement. The shift collar is movable between a high range position in which the shift collar connects the input shaft from the first main section directly to an output shaft and a low range position in which the shift collar connects the input shaft to the output shaft through a gear reduction arrangement. The shift collar arrangement can have internal teeth that constantly engage external teeth on the output shaft. If the shift collar arrangement is moved axially along the output shaft out of a neutral position to the high range position or the low range position, the internal teeth on the shift collar can also engage external teeth on either the input shaft or the gear reduction arrangement.
The synchronizer arrangement is movable by the shift collar and is typically provided to assist in shifting from low range to high range, or vice versa. Synchronizing clutch assemblies of this general type are available from Mack Trucks, Inc., identified as Part No. 320 KB3147 or 320KB3150. U.S. Pat. No. 6,571,927 also discloses a synchronizing arrangement of such a general type and is incorporated by reference.
In an illustrative synchronizing arrangement of this type, first and second synchronizer cones with external friction surfaces are spaced by pins that extend through apertures in a shift collar disposed between the cones. The pins include a first set of pins with tapered surfaces tapering from a larger diameter to a smaller diameter in the direction from the first synchronizer cone to the second synchronizer cone and a second set of pins with tapered surfaces tapering from a larger diameter to a smaller diameter in the direction from the second synchronizer cone to the first synchronizer cone. Springs are disposed in recesses in the shift collar and bias the surfaces of the apertures of the shift collar against the surfaces of the pins when the shift collar and the synchronizer cones are rotated in a direction corresponding to forward.
When shifting ranges, the external friction surfaces of the first or second synchronizer cones first contact an internal friction surface on mating synchronizing cones associated with a high range or a low range position of the synchronizing arrangement. As the synchronizing cones are brought closer together and approach the same rotational speeds, at least some of the springs in the shift collar are initially in contact with the smaller diameter portions of the pins so that there is a limited amount of play between the synchronizing cones and the shift collar. When the internal teeth on the shift collar are about to engage the external teeth on the input shaft or the gear reduction arrangement, the springs contact the tapered surfaces of the set of pins associated with high range or low range, respectively, simultaneously tending to resist further movement toward the high range or low range positions and reducing the amount of play possible while the mating synchronizing cones arrive at rotational speeds that substantially match. After the synchronizing cones arrive at matching rotational speeds, which typically occurs when the shift collar has been moved against the force of the springs so that the springs press against a large diameter portion of the set of pins, the internal teeth on the shift collar can safely engage the external teeth on the input shaft or the gear reduction arrangement without substantial risk of tooth damage due to the different speeds of the input shaft or gear reduction arrangement and the output shaft.
The springs in the shift collar are arranged to facilitate indexing of the internal teeth on the shift collar and external teeth on the input shaft or the gear reduction arrangement but are oriented so that they resist movement of the shift collar relative to the synchronizer cones only when the components are being urged in a rotational direction corresponding to a forward direction. When the main transmission is in reverse gear, the input and output shafts rotate in opposite directions than the rotational direction corresponding to a forward direction and, during shifting of range from low to high or high to low, the springs in the shift collar do not urge the surfaces of the pins against the surfaces of the apertures in the shift collar. The springs, therefore, do not facilitate bringing the synchronizing cones up to the same speeds before engagement of the teeth on the shift collar and the input shaft or the gear reduction arrangement. As a consequence, the gears can clash during a range shift in reverse, damaging the “coast sides” of the teeth, i.e., the sides of the teeth that are not in contact during rotation corresponding to a forward direction and that are in contact during rotation corresponding to a reverse direction. Damage to the coast sides of the teeth can damage the case hardening of the teeth and result in smearing of teeth on their drive sides, as well. With damage of this type, it has been observed that the transmission can jump out of range.
It is desirable to provide a transmission arrangement that can prevent a range shift in an auxiliary portion of a transmission when a main portion of the transmission is in reverse gear.
Many vehicles currently on the road do not have any arrangement to prevent an operator from making a range shift when the vehicle is in reverse gear. It is desirable to provide an inexpensive and simple retrofit arrangement for a transmission arrangement that can prevent a range shift in an auxiliary portion of a transmission when a main portion of the transmission is in reverse gear.
In accordance with an aspect of the present invention, an arrangement is provided for inhibiting axial movement of a range clutch in a transmission, the transmission comprising a main shaft and an output shaft, the range clutch being movable on the output shaft between a high range position and a low range position to modify a main shaft rotational speed to at least one different output shaft rotational speed, and a plurality of selectable gears comprising a forward gear and a reverse gear for providing different speed ratios between an input shaft and the main shaft, the main shaft rotating in a main shaft forward rotational direction and in a main shaft reverse rotational direction when coupled to the input shaft and in the forward gear and in the reverse gear, respectively, the output shaft rotating in an output shaft forward rotational direction and in an output shaft reverse rotational direction when coupled to the main shaft rotating in the main shaft forward rotational direction and in the main shaft reverse rotational direction, respectively. The arrangement comprises a driver adapted to move the range clutch axially on the output shaft between the high range position and the low range position, a sensor arrangement adapted to sense at least one of reverse rotational direction and potential reverse rotational direction of at least one of the main shaft and the output shaft and to generate an inhibit range shift signal upon sensing at least one of reverse rotational direction and potential reverse rotational direction, and a controller adapted to inhibit operation of the driver upon receipt of the inhibit range shift signal from the sensor arrangement.
In accordance with another aspect of the present invention, a method is provided for inhibiting axial movement of a range clutch in a transmission, the transmission comprising a main shaft and an output shaft, the range clutch being movable on the output shaft between a high range position and a low range position to modify a main shaft rotational speed to at least one different output shaft rotational speed, and a plurality of selectable gears comprising a forward gear and a reverse gear for providing different speed ratios between an input shaft and the main shaft, the main shaft rotating in a main shaft forward rotational direction and in a main shaft reverse rotational direction when coupled to the input shaft and in the forward gear and in the reverse gear, respectively, the output shaft rotating in an output shaft forward rotational direction and in an output shaft reverse rotational direction when coupled to the main shaft rotating in the main shaft forward rotational direction and in the main shaft reverse rotational direction, respectively. The method comprises sensing at least one of reverse rotational direction and potential reverse rotational direction of at least one of the main shaft and the output shaft and inhibiting movement of the range clutch axially on the output shaft between the high range position and the low range position.
In accordance with another aspect of the present invention, a method of retrofitting a transmission to inhibit axial movement of a range clutch in the transmission is provided, the transmission comprising a main shaft and an output shaft, the range clutch being movable on the output shaft between a high range position and a low range position to modify a main shaft rotational speed to at least one different output shaft rotational speed, and a plurality of selectable gears comprising a forward gear and a reverse gear for providing different speed ratios between an input shaft and the main shaft, the main shaft rotating in a main shaft forward rotational direction and in a main shaft reverse rotational direction when coupled to the input shaft and in the forward gear and in the reverse gear, respectively, the output shaft rotating in an output shaft forward rotational direction and in an output shaft reverse rotational direction when coupled to the main shaft rotating in the main shaft forward rotational direction and in the main shaft reverse rotational direction, respectively, wherein the range clutch is adapted to be moved to the high range position and the low range position by positioning a range shift valve in a high range shift valve position and a low range shift valve position, respectively, so that a source of hydrostatic pressure is adapted to communicate with a high range chamber and a low range chamber, respectively, of a range cylinder, the high range chamber and the low range chamber being defined by a piston movable in the range cylinder, the piston being connected to the range clutch. The method comprises providing a sensor arrangement to sense at least one of reverse rotational direction and potential reverse rotational direction of at least one of the main shaft and the output shaft and send a signal to a controller when at least one of reverse rotational direction and potential reverse rotational direction of the at least one of the main shaft and the output shaft is sensed, providing an openable and closable range shift inhibitor valve for opening and closing flow communication between the source of hydrostatic pressure and the one of the high range shift valve chamber and the low range shift valve chamber, and programming the controller to output a signal in response to the sensor arrangement signal, the controller signal controlling opening and closing of the range shift inhibitor valve.